Recoil (often called knockback, kickback or simply kick) is the backward momentum of a firearm when the firearm is discharged. Recoil is the physical manifestation of the momentum opposing the forward momentum of the projectile and exhaust gases (ejecta), according to the conservation of momentum (Newton's third law). This change in momentum of the ejecta results in a force that must be compensated for by the shooter. In order to bring the gun to a halt, a forward counter-recoil force must be applied to the firearm. Generally, the counter-recoil force applied by the shooter is smaller than the recoil force, and is applied over a time period that is longer than the time that the recoil force is being applied (e.g., the time during which the ejecta are still in the barrel of the gun). This imbalance of forces causes the gun to move backward until it is motionless, and may result in the gun kicking upward as the momentum is transferred to angular momentum around a joint of a shooter. For small arms, the way in which the shooter perceives the recoil, or kick, can have a significant impact on the shooter's experience and performance.